1. Technical Field
The disclosure relates to power supply circuits, and particularly to a power supply circuit for supplying electric power to a portable computer.
2. Description of Related Art
As our world becomes more technologically advanced, the demand for electrical power becomes more sophisticated. Conventionally, portable computers, such as laptop and notebook computers, are powered either through an AC adapter or through a rechargeable battery, such as a nickel cadmium (NiCd) battery or a nickel metal hydride (NiMH) battery. The AC adapter needs to be connected to a fixed electrical outlet via electrical lines and thus is not convenient for outdoor use. As batteries continue to be designed and developed to have greater capacity, the use of batteries to power portable computers has become increasingly common.
If a user anticipates to operate the portable computer for an extended period of time where AC power source is unavailable, the user typically provides one or more charged backup batteries. The portable computer normally has a function for displaying a remaining capacity of the main battery to the user. If the remaining capacity of the main battery is less than a preset value, the user is warned of a low battery condition. At this time, the user can draw the main battery out of the portable computer and install the backup battery into the portable computer, to avoid a sudden shutdown of the portable computer during use and obtain an extended use period.
However, when replacing the main battery, firstly, the portable computer must be manually shut down and the battery drawn out. Then the portable computer must be restarted after the backup battery is installed. Otherwise, information such as the datas that files are saved may be lost. Thus, replacing the main battery is troublesome and inconvenient for the user.
It is thus desirable to provide a portable computer with a power supply circuit which can overcome the described limitations.